The present invention is a continuous multi-stage counter current device for contacting 2 immiscible fluids of different densities or contacting fluids with gases. Solids may also be present in the liquid phase. It can be used as a reactor but the primary purpose is as an extractor for recovering high value materials or removing impurities from a process fluid. Applications include but are not limited to industrial processing of chemicals, pharmaceuticals, food materials, minerals and natural products.

The method and equipment described here involves contacting two immiscible fluids of different densities which are referred to as light fluid and heavy fluid respectively. Multiple stages are arranged in a vertical cascade and each stage has a mixing zone and a separation zone. The separation zone is divided into two partitions. Light fluid is fed continuously at or below the lowest mixing stage and heavy fluid is fed continuously at or above the highest mixing stage. Light fluid flows up through the cascade and heavy fluid flows down. Counter current flow occurs due to the density difference and immiscibility of the two fluids. Maximum interfacial contact between the fluids occurs in the mixing zones. The light and heavy fluids separate in the unmixed separation zones. A third component referred to as the solute may be present in the feed stream of either the light or heavy fluid. The solute may be a single compound or multiple compounds. When the light and heavy fluids are contacted in the mixing zone, the solute is distributed between the light and heavy fluids. The ratio of solute dissolved in light and heavy fluids at equilibrium is dictated by the partition coefficient. In practice, partial equilibrium is achieved. When the apparatus is used as an extractor it can be used to transfer solute from the light fluid to the heavy fluid or vice versa. Counter current extraction through multiple stages as described here delivers high extraction efficiency and efficient use of wash fluid. Background theory is covered in literature.

Extractors with multiple stages where each stage has an actively mixed zone and a separation zone are known. The stages are arranged in a vertical cascade to eliminate the need for pump transfer between stages. A single mixer drive shaft serving all the mixing separation stages is used. Radial baffles above and below the mixing stages reduce turbulence in the separation zones and process fluid passes through apertures in these baffles. US patent 2,665,196 describes a multi stage extractor with these characteristics. An extractor by Sulzer operates on the same principles but uses the added feature of weirs to increase the retention time of light fluid at the top of each separation zone. This gives improved phase separation and therefore more efficient extraction. The Sulzer design is the nearest prior art identified.

The novel features of the device of this invention is that each separation zone is segregated into two axial separation partitions. Flow of light fluid up to the next higher mixing zone is unidirectional through one or more dedicated apertures in the radial baffles that separate the stages in the cascade. The flow of heavy fluid down to the next lower mixing zone is unidirectional through one or more dedicated apertures in the radial baffles that separate the stages in the cascade. This arrangement reduces back mixing and gives improved capacity and higher separation efficiency.

The phrases light fluid separation zone and heavy fluid separation zone are used for clarity here. It should be noted that light and heavy fluids separate in both separation zones. The light fluid separation zone has higher ratio of light fluid compared to that of the heavy fluid separation zone.

The description mixer settler is used to describe each stage. Separation is used in the detailed description and refers to separation of the light and heavy fluids.

Figure 1 shows a multi stage counter current extractor of this invention. The body of the extractor comprises of a tube or series of tube sections as shown joined to form a sealed system. The top section 9 is the final separator for the light fluid. The bottom section 5 is the final separator for the heavy fluid. These final separators are optional and may be done in separate equipment. Between the top and bottom separators are four mixer settler stages each one having a mixing zone 7 and a separation zone 6. A minimum of two mixer settler stages is required for counter current extraction but more stages give more efficient the extraction. Three or more mixer settler stages are preferred and five or more mixer settler stages even more preferred. Ten or more mixer stages are used where high extraction efficiency is required. Light fluid addition 3 is introduced at or below the lowest mixing stage. Heavy fluid addition 2 is introduced at or above the highest mixing stage. Light fluid is taken off above the highest mixing stage and preferably above the heavy fluid addition point. The drive motor 10 rotates the mixer shaft. This is mounted at the top or bottom of the cascade and a single shaft can extend to all the mixing stages. The locating pin 8 aligns and or supports the cascade internals but alternative methods can be used for this need. The terms left and right refer to the diagrams but in practice left and right will depend on the angle of view. Each separation zone has a right and left handed radial baffle plate located at the top and bottom of the separation zone respectively. Figure 2 shows a right handed baffle plate 11. The separation zone feed apertures 12 are shown on the left. These carry light fluid up into the separation zone from the mixing zone below and allow entrained heavy fluid to settle back to the mixing zone. The separation zone discharge aperture 13 is shown on the right. This is sized to maintain unidirectional flow of heavy fluid passing from the separation zone down into the mixing zone. This aperture 13 can be cut directly in the plate. The plug as shown is preferred as this allows the aperture size to be varied without changing the plate. The mixing shaft aperture 14 is on one side of the plate and may have a collar 14 to support and or stabilise the mixer shaft. It is preferred that the baffle plates have a seal at the perimeter wall which can be done by different means. The left handed plate is located below the mixing zone and has the feed and discharge apertures on opposite sides to the right hand plate. The preferred solution is with a single mixer shaft 16 for all stages but separate dedicated side entry mixer shafts for each stage can be used.

Figure 3 shows a cutaway view of the mixer settler stage. The tube body 17 forms a sealed system. Radial baffles are located at the top 21 and bottom 11 of the separation zone. These two baffle plates are opposite handed. The axial partition plate 19 divides the separation zone in two sub zones referred to here as the light and heavy separation zones respectively. The heavy separation zone has the discharge aperture at the bottom and the light separation zone has the discharge aperture at the top. The partition plate uses wall seals 18 to prevent cross mixing between the partitions. The partition plate 19 also forms a seal with the top and bottom baffle plates 21 and 11 respectively. Different methods for sealing can be used including close tolerance or soft seals 18 as shown. A mixer shaft 16 passes vertically through the tube body 17 and passes on one side of the partition plate 19. The mixer shaft can be on either side of the partition plate. The mixer blade 15 is rotated by the agitator shaft 16.

It is preferred that the discharge aperture for the heavy separation zone is sized to maintain unidirectional flow of heavy fluid down to the next lower mixing zone. The discharge aperture at the top of the light separation zone is sized to carry unidirectional flow of light fluid up to the next higher mixing zone. The size of these apertures will vary according to system size and fluid properties. It is also preferred that the light fluid discharge aperture is sized to hold back a layer of light fluid under the radial baffle plate. It is preferred that the radial baffle above the top mixing stage in the cascade has feed apertures across the full diameter of the tube body giving the maximum open area for the flow of light fluid up and heavy fluid to return to the mixing zone. It is preferred that the baffle below the bottom mixing stage in the cascade has apertures across the whole face.

The static head in the light separation zone is lower than the static head in the heavy separation zone. This head difference promotes unidirectional flow through the light separation zone discharge aperture. The degree of resistance through the light fluid discharge aperture determines the amount of light fluid accumulated in this separation zone. The height of light fluid leg in the light fluid separation zone should be less than 100% of the full height of said zone.

The discharge aperture for the light fluid separation zone can be of fixed geometry as shown in figure 2. Variable geometry discharge apertures for the light fluids are preferred. Various options can be used. Figure 4 shows a hinged cap discharge aperture 22 for the light separation zone. Figure 5 shows a rising plug discharge aperture 23 for the light separation zone. The open area of flow for the cap or the rising plug increases as the plug rises. The density and weight of the hinged cap or rising plugs are selected to hold back a layer of light in the light phase separation zone. This provides additional hold up time of light fluid to ensure efficient disengagement of light fluid from heavy fluid. A small leak path in the hinged cap or rising plug is preferred so that the system discharges all the light fluid at the end of the cycle.

Dimensions of the system cannot be specified here as these will vary according to required flow capacity and properties of the fluids.

The flow of fluid into the light separating zone is bidirectional due to the return flow of heavy. The flow of heavy fluid into heavy separating zone is bidirectional due to the return flow of light.

The light fluid is feed 3 is fed at a controlled rate. This can be regulated by a metering pump or a flow meter with control valve. The heavy fluid feed 2 is fed at a controlled rate. This can be regulated by a metering pump or a flow meter with control valve.

It is preferred that the flow heavy fluid discharging from the cascade 4 is controlled by a pump or control valve using a signal from an instrument which maintains the required heavy fluid level in the top stage of the cascade. It is also preferred that this is done using a static leg connected to the tube body by side connections above and below the desired level control point. The preferred level control point for heavy fluid lies within the top mixing stage.

It is preferred that the light fluid discharge is regulated by the difference in flow between the feed fluids 2, 3 and the heavy fluid discharge 4.

Design variations can be employed such as baffle covers over the light fluid discharge aperture. Coalescing elements can be used to improve separation in the light and heavy separation zones. Double baffle plates can be used. The tube body 17 may have an external jacket through which passes heat transfer fluid for adding or removing heat.

Figure 3 shows the partition plate 19 dividing the separation zone into two sub zones of equal volume. The partition plate 19 may also divide the separation zone into two sub zones which are not of equal volume.

It is preferred that the feed apertures of the light fluid separation zone have a cross sectional area which is 10 times greater than the discharge aperture. It is preferred that the feed apertures of the heavy fluid separation zone have a cross sectional area which is 10 times greater than the discharge aperture.

An example of the use of a contactor/separator of this invention is in the need to remove impurities following a chemical reaction. For example the reaction may produce a desired chemical such as a pharmaceutical intermediate in an organic diluent and may also contain impurities such as reactant residues or catalyst residues (which may be water soluble). Where the organic diluent is a light fluid it together with the impurities it contains may be fed to the bottom of the contactor and water may be fed to the top of the contactor. The combination of the mixing and separation provided by the device of this invention enables transfer of the impurities from the organic phase to the aqueous phase whereby the purified organic phase containing the desired chemical is retrieved at the top of the cascade.

Clearly the invention is equally useful in situations where the desired material is in the heavier fluid and the impurities are extracted by the lighter fluid. The purified heavier fluid being retrieved at the bottom of the cascade.